The present invention relates to an address transition detecting circuit which detects a transition of an address signal. The address transition detecting circuit is composed of a memory circuit such as a static random access memory.
FIG. 6 is a circuit diagram showing the conventional address transition detecting circuit. This address transition detecting circuit 500 comprises a plurality of address signal transition detecting circuits 500-1 to 500-n and an OR circuit 503.
FIG. 7 is a circuit diagram of one of the address signal transition detecting circuits 500-1 to 500-n. The address signal transition detecting circuit 500-1 comprises a delay circuit 505 and an exclusive NOR gate 507. The delay circuit 505 has an input terminal connected to a node a which is connected to an address signal line and an output terminal connected to a node b. The delay circuit 505 receives an address signal on the address signal line and outputs a delayed address signal to the node b. The exclusive NOR gate 507 has two input terminals connected to the node a and the node b respectively and an output terminal connected to a node c. The exclusive NOR gate 507 receives the address signal and the delayed address signal and outputs an address transition pulse to the node c in response to the address signal and the delayed address signal.
Referring back to FIG. 6, the OR circuit 503 comprises n-type MOS transistors 511-1 to 511-n, a p-type MOS transistor 509 and an invertor 513. The gate of the MOS transistor 509 and the sources of the MOS transistors 511-1 to 511-n are connected to a ground. The source of the MOS transistor 509 is connected to a power supply. The drain of the MOS transistor 509 and the drains of the MOS transistors 511-1 to 511-n are commonly connected to an input terminal of the invertor 513. The gates of the MOS transistors 511-1 to 511-n are connected to the address signal transition detecting circuits 500-1 to 500-n respectively.
The invertor 513 outputs a "H" level signal when at least one of the MOS transistors 511-1 to 511-n receives the address transition pulse.
In the conventional address transition detecting circuit described above, the number of the n-type MOS transistors 511-1 to 511-n of the OR circuit 503 depends on the number of the address signal lines. Where the conventional address transition detecting circuit 500 has a lot of address signal lines, the OR circuit 503 has a lot of MOS transistors and therefore needs a large circuit area.